Envelope coating method and apparatus



Aug.'-8, 1961 G. w-:ls'Tl Erm.:

` ENvELoPE oATING METHOD AND APPARATUS "2 sheets-sheet 2 Filed im.. z8',4 1957' llumml v s n f 239531453` g coATING METHOD AND APPARATUS' E NvELoP George Meister, Newark., -and Stanley -'A. Lopenski,

PomptoniPlains, NJ., assignors to .Westinghouse Electric Corporation,` East Pittsburgh, P a., a corporation of Pennsylvania Filed Oct. 28, 1957, Ser. No. 692,841 1 2 Claims.' (Cl. 117-417) This i-nvention relates toa method and apparatus for coating envelopes and, more particularly, to a method and'apparatus for improving the adherence of electrostatically-deposited, light-scattering coating materialsv to incandescent `lamp envelopes.

' Incandescent lamp envelopes )are desirably provided Patented Aug. 8,1961

It is an additionalobject to provide an improved incandescent lamp envelope electrostatic coating apparatus for producing l-amp envelopes with very-adherent coatings.

` The aforesaid objects of the invention, and other objects which will become apparent as the description pro# ceeds, are achieved by providing a follow-up, travelling,

electrostatic field for a minimum'specified time to the coated envelope, which follow-up ield=increases the adherence of thev electostatically-deposited, finelydividecl coating material to the interior surface of the envelope.

Also provided is an improved apparatus which incorporates a follow-upevoltage station wherein a travelling, follow-up electrostatic eld is applied between the envelope with a coating onfthe inner envelope surface, vwhich coating normally comprises aiinely-dividedflight-scattering coating material which provides the lamp, when incandesced, with a very even appearance. The most-com monly-used coating material'is' finely-divided silica and an electrostatic apparatus lfor depositing such..material.onto

Athe inner surfacev ofan incandescent lamp envelope is described incopendingv application Serial No. 603,636, tiled Augustl 1 3, 1956, now Patent No. 2,811,131, titled "Electrostatic Coating Machine. fo'r Incandescent Lamp Envelopes, by Lopenski, Meister andWa'ino', of which Lopenski and Meister 4arefthc coinventors herein, and owned ,by thepresent assignee. l 4

When light-scattering materials, such as silica, are depositedby-'thc electrostatic apparatus described in this aforementioned copending application, troubles are somesurface 'and an electrode which reciprocates into the interior of the envelope. l

For a better understanding of the invention, reference should be had t'o the accompanying drawings where:

`FIG. l is a diagrammatic plan view of the improved i electrostatic coating apparatus;

FIG. 2 is anvelev'ational view, partly in section,taken at the tirst coating position shown in FIG. l;

FIG. 3 is an elevational view, partly in section, taken I at the rst followup-voltage position shown in FIG. 1.

deposited, finely divided coating material to the interior surface vof any type 4of envelope, they are particularly' times encountered with respect to suicient adherence of the coated silica to the envelope. -Normally the adherence is quitel satisfactory, 4but the ymargin of safetyvbetween satisfactory and .un'sati sfact ory adherence is not as great as desired, with the result that slight rnis'adjustments -of the equipment may resultv incoatngs which are not satisfactory with respect toadherence.' A coating which is poorly adherent to the lamp envelopenormally manifests itselfin the forx'nof blow-ofs' whichare encountered during the manufacture of the lamp. In explanation, after the envelope hasbeen coated,. a'. reentrant stem' press is sealed tothe neck' portion. Thereafter thel en'- velope is evacuated Aand vtilledwithV an inert gas which is inserted through a tubulation which'o'pens intothe lamp envelope at .a location proximate the envelope neck.

While the method and apparatus described hereinafter are useful for increasing the adherence of electrostaticallyuseful for improving the adherence of such material, and particularly silica, to the interior surface of incandescent lamp envelopes and hence they have been soi'illustrated y and will be sodescribed.

. With-v specific reference' to the form of the invention illustrated in the drawings, in -FIG. vl is shown in diagrammatic forman electrostatic coating machine 10. This vmachineand the operation thereof may be identical with that machine disclosed in' heretoforeLmentioned-Patent No. 2,811,131, which maybe referred to for details, ex-

cept that a follow-up-voltage 'work station, described in detail hereinafter, hasbeen added. The electrostatic coating machineA 10 generally comprises a stationary table 12 having mounted thereon an indexing conveyor unit 14',

`which conveyor carries a plurality of bulb-receiving and "bulb-retaining heads 16 through a plurality of work stations, as described hereinafter.

These conveyorcarried heads 16 are adapted Ato be indexed sequentially between each of the individual positions located about the table 12 .and to remain for al predetermined period at each of thev With ar poorly-adherent coating, the puff of ll gas` which emanates from the .tubulation intothe -envelope has a tendency to blow off a small areaof the coated, lightscattering material. These so-called -vblowol'f` areasf are deleterious to the appearance of the" completed lamp.

. Also, the presence offblowwtf areas" in theneck portion "of theenvelopes is indicative that the general adherence'ofthe coatingl to th envelope may be unsatis Y factory.` It is lthus desirable to' .insure thatthe adherence .of the light-scattering, envelope eoating .mat erial is al'- ways satisfactory even Athoughlslight'misadjustments of' the coating equipment may occur; .A

It is the general, object of .this invention to provide'a l. method for increasing the 'adherence of velectrostaticpallydeposited, tinely-dividedcoating material tothe interior surface of an envelope. v

It is a further object to provide a method for increasing the adherence of" electrostatically-deposited, finely-di-v vided, light-scattering coatingmaterial, preferablysilica, to the'interior surface of anincandescent lamp envelope.

It is another object to'provide a method forfelectro` positions. In the embodiment as shown, there are thirty such positions. Indexing is accomplished by means of a motor-driven indexing drive 18 whichin turn connects to a sprocket drive 20 and driven sprocket 22, which index the conveyor 14 Aabout the table 12. The driving motor 24 for the indexing drive 18 also connects to `a camshaft 2 6, so that the'motions of the individual cams carried by the shaft 26 are synchronized with the indexing of the heads 16 about the table 12. 'The envelope-carrying portion of eachof the individual headsl' is adapted'to `be rotated v with respect to the table 12 and this rotation is accomplished by a m'otor drive 28 which connects to the individualheads 16 by a belt 3'0to effect a rotation of the lamp-envelope-carrying portion of the vheads 16.

In the 'operation of the electrostatic coating machine,

' `uncoated envelopes are loaded at the .loading station 32,

statically depositing a coating `of finely-divided, lightf'scattering'silica particles onto the interior surface of an incandescent lamp envelope so that the deposited silica will have very good adherence to the envelope.

either by hand or by an automatic transfer mechanism,

`such as are commonly used..l Thereafter, the uncoated envelopes are :indexed through a preheating work station `34, which may comprisefthree positions for example,

where they are heated by gas-air burners 36 and may be simultaneously flushed with air in order to remove any lint.

tive. In explanation, it is well known that glass has Preheating of the envelopes is required in order to render them substantially uniformly electrically conduc! 'a negative temperature coetiicient of resistance and thatv heating `glass will cause :it vto become relatively electrically conductive. As a speciic-examplq vfor a soda-limc-y silica type glass, a preheating -Atemt'aerature of 100 C. is quite satisfactory to cause thc.4 envelopes to ybecome substantially 'uniformly electrically conductive -for the intended purposes. 'This preheating temperature may; `b c varied over a wide range if .desired,.asthe degree kof preheating is not critical. Desirably the uncoated envelopes. v are rotated at the preheating 'work' station 34 with reassuma l envelopesby virtue of 'the ionized 'nature of the gas spect'lto the gas-air burners inorder'to etfect uniform preheating, but if desired, thegpreheating c ould'be effected by infrared-,type heaters, utilizing `an infraredheating tun-- nel where rotation of .the-envelop es, with respect' lto vthe table' 12 could. be" eliminated. Thereafter the. preheated envelopes are indexed through they .coating work;A station 38, which may'A comprise two positions for'example and through. the followup-voltage work station 4 0, iwhich may comprise two positions r f ir example-, The envelopes arethen indexed through thenlfehring wor-kv -sta' tion'47., fy

which` may comprisejseven positions for example. At

flame. lPreferably the negative side ,of the high-voltage D.C. potential is connected t'o the `nozz-le conduit 76 with the other side of the high-voltage. DzC. supply being connectedgtoth'e gas-airhurners 181, one of which is provided at each position `of the coating station 38. Preferablythe gas-air burners `are grounded :to minimize shock hazard. The'DC. ysupply .may he veither pulsating or ,steady with respect to voltage, vbut from the standpoint -ofeconQmy it is desirable tol use a lpulsatinghigh-voltage,

Adirect-current supply lwhich may be variable from about t8 to about 25 kilovolts, for example. Even in the case the lehring work-station 42,1fsuhstautiallyall residual moisture is removed fromgthe .coated-envelopes by means of an infrared-heated jlehring tunnel 43, while `simultane-` ously blowing.hot,' dry air thi'ough `the'interior of .the coated envelopes. [Afterflehring, the coated envelopes are indexedto the unloading. station .44 vwhere they may.:

be unloaded either by hand- ,orbyconventional automatic transfer mechanisrn. If desired,- -the preheat, coating and ll`ehring stations mayv be` identical with-those as described in the' aforementioned'fPatent No.` 2,811,131. A head l16, when indexed to lone' .position .of the coating work station -'38,-is shown' inelevational view in FIG. 2. Each` head 16 mayv -cbe ,identicalf' and .generally comprises a hollow chuck 46` made ,of 'a--lrefralctory material such as lava and conformedto receive 4theneck' rportion-48 of the, envelope S to-retain-sa'rne throughout the coating operation'.` Each envelopes() is generallysymmetrical and comprises 'a `bulbous portion SZEterminating-in the neck.por'tio n :.48 whicliisfopen at this state of the lamp 7 manufacture.v The chuck k46 of. each head 16l is lsecured to a metal bearing 54'which rides within a journal bearing 56l to facilitate `rotation of the lava ,chuck 46 with respect'to the tribale-1,2.` "Each of ,the-heads 16 is hinged 'together through an extension 58 of the vjournal bearing z of a pulsating 1D.C. voltage, the resulting integrated electrostatic field `will-bel unidirectional. As a specic example, for .an envelope designed for a 100 wattlamp,

'the D.C, voltagecmay be 15 .kilovolts.

When the nozzle :78 is reciprocated into smoke-delivering position within the envelope y5l), a gaseous medium such as' air, carrying a smoke ,of finely-divided, light-scattering `material s -uch as'silica, `is forced from the smoke generator (not shown-)ythrough the flexible feed conduit V- 80 into the nozzle feed conduit '7=6 and through the nozzle 78. This charges at least a portion ofthe finely-divided,

' Ylight-scattering material `vandsimultaneously the highvoltage D.C. isl appliedbetween the nozzle feedl conduit 76 and the gas-air' burner 81.y This causes a strong electrostatic yfeldto be setup between the conducting nozzle 78 and'.electrode 79 positioned with the interior of the yenvelope v50 and `the -electrica'lly-conducting surface of theenvelope ASt) and va substantial p ortion of the iinely-divided material which forms the smoke is directed f to the envelope wall where it adheres.' In the case of silica, it has been found that approximately of the silica which is injected into the envelope asv a smoke is deposited thereon. The remainder .of the silica smoke which is not deposited is carried by the gaseous medium 56 toform the conveyor V14 and in FIG. 2 these extensions 58 have been shown offset from their actual Apositioning for purposes o f illustration. A pulley 60 co'nnects to the bearing 54 to cooperate with belt 30 to facilitate rotation of the lava chuck 46 with" respect to the table 1 2. A blow-back manifold 62 -is provided at the coating station 38 for the purpose of blowing undepo'sited coating material from the supply conduits and aforementioned Patent No. 2,811,131 lis referred to foi' details.

As each ,envelope-carrying head `116 isindexed to the coating station '33, the coating lift lcam .64 (see. FIG. l) actuates a push rod66 which connects `to -a vguided reciprocating bar 68 'and ywhich inturn connects to -the nozzle .and return-conduit assembly/"70. An upward move- .ment ofthe 'push rod 66 causes'the nozzl'eand returnconduitassembly 70.1to move into smoke-delivering pofrom the -envelope 50,1 through the smoke-return conduit 72 and throughthe blow-back-tube 74, rwhere the undeposited smoke may be collected' for further use. After the nozzle has been insmoke-delivei'ing position for one second, rfor example, the lift cam 64- has rotated suiciently that the 'return-.conduit and nozzle assembly 70 `is retracted from its'position `within the head 16 and the envelope-carrying head 16 is indexed to the next station.

Inthe diagrammaticview'shown in FG.. l, two individual coating positions have been provided for applying the Alight-diffusing coating :to the envelopes. In practice, it is often desirable to-use oni-y onev of the individual coating positions and in such case, the unused coating po- `sition is not actuatedd'uring the coating operation. Thus the coating work station 38 maybe compriseone or more individual similar positions, if desired.

yIn order tha'tfthecoating material will .be deposited in aluniformv manner'on the-envelope `S0, it is necessary to sition within the head-carried envelope 50. The nozzle and return-conduit 'assembly 70 generally comprises a hollow, cylindrical return conduit 72 which is fabricated of non-conducting material such as porcelain, for example, and which `connects to' a exible1 powder-blowback conduit 74.' lThe nozzle feed conduit v76 is colaxially positioned within the'return rconduit 72 and is fabricated of electrically conducting material such as brass. The upper portionof the nozzle feedyconduit Y 76 terminates in a smoke-dilusing orifice or nozzle 78 which may-.carry van `electrode `79. The lower end of the nozzle conduit 76 yis connected to a ilelriblefeed conduit 80, which in turn' connects vto a ysmoke-generator. unit (not shown) 4which is adapted to generate a smoke of effect a rotation between the' nozzle 78 and the envelope 50 while the smoke is blown into the envelope and while theelectrostatic ield'is -applied to cause a substantial 'portion of the material comprising the smoke to deposit on the envelope. This is desirably accomplished by rotating the envelope 50 during ycoating with respect to the table` 12 and with respect to the gas-air burner-8l.

Since the envelope 5 0 is substantially uniformly electrically conductive, the electrostatic field `which is applied from the electrode to the surface of the envelope is evenly distributed.

After the envelopes have been coated, the envelopecarrying heads 16 are indexed to the lfollow-up-voltage work station 40, one position of which is shown in detail in FIG. 3. A follow-up-voltage..liftcamz'82 (sec FIZG." l

1) actuates a pushrod .83 which connects to. a reciproeating bar v84-and which` in `turn connects: to a guided `electrode 86. An.upwar'dfmovement.of the push'rod used in the initial coating,` isvapplied. between the. moving electrode 86 and the conducting surfaces of the envelope 50 by means ofi the-. .gasz-arrburners 88, one of. which is providedat each'positionof th'e..followupyoltage station 40 to maintain"theenvelopesr at this fwork station substantially `uniformly. electricallyv conducting; and to facilitate electrical.'contactgtov the surfaces; of.A the envelopes. During..the application of. the electrostatic field and while the: electrode 86. travels withinl the .envelope 50,l the envelope sf'rota'ted with. r'espect: to the stationary gas-air burnerl 88. ini'o'r'der to". maintain .same substantially uniformly` electrically conductive.so that. the electrostatic field which-.is applied between'the' electrode.- 86 and the envelopev surface is evenly distributed-g.. The speed of rotation of the. envelopemay be: 180 r.p.m. forexample,y and. this` speedof/ rotatiom may., be varied. considerably. f

Alternately, they envelope 50""conldf`bc held. stationary if .desired and the gas-airfburner.rotated thereabout. during the 'applicationr ot' the.: follow-um electrostatic field in order to achievey the.- same effects. 'R'otating-y gas-air burner arrangements arev frequently." us'edA in the' lampmaking-equipmentart; yAlso,.the envelopev and gas-air burner could be. held.stationarywithirespectto one an'- other during the'applicationoofzthe follow-"upy electro-` static field. Such.' an-embodir'nent;. however, would normally necessitate an encircling-.type 'ofgas-air heaterso that the surfacesv ofthe envelopewould. besubstantially uniformly heated and? so that the-foll'o.w-up` electrostatic field wouldbeevenly'distributedl.

The electrode 86 desirably.;isreciprocatcdinto theen- 'velopeSt)` withancven motion and?. the follow-up'electrostatic ieldfdesirablyis applied. between the electrode 86 and. the conducting envelope' 50i for the4 entire period i thtazanypart ofv the electrode 86`fisfmoving within the enevlopc 50. The'electrostaticifieldapplied between' the electrode`86`an'd the substantialy uniformly. electrically conductive.'envelopesris actually moving or travelling inl nature sincethe electrodeand conductive envelope have a-rlelative motion: therebetween. The travelling electrostatic field willfnormally vary somewhat in intensity since the spacingbetween thezu'ppermose portion-'of the electrode andl the envelopesurface'will vary-as the-electrode is moved'witl'iinA the interior offthe'cnvelope. Such. yvariations in field intensity are not objectionable..l Thus .the travelling. electrostatic'fieldk isl actually applied betweenthe. surfaceof the envelope 50` and`a plurality of locations whichl are'. within: the. envelope. preferably extending frfom' a. locationiproximate the mid-point of' the envelope neck-portion. '48? to. a-location proximate the maximum` diameter of thefbulbous portion-52 of theen- {elopej.,5 0`. In `thepreferred'..enibodiment aslillustrate'd, the electrode'I traverses tf'relgcenterl line' of theenvelope. The electrode. maybe offsetA slightlyyif. desired, although care should be taken;so.that= theelectrode does not con- I i tact thefenvelope'; coating or; `it willi tend to knock ofi coating. material; Al'so;the zelectrode186- may be reciprocatedl to an extreme position: well within. the coated venvelopej 50, eventapproaching.thewuppermost bulbons to the cnevlop'c to be improved-.to the, required degree.

Proper timing of the` applied follow-up voltageV may be accomplished by. applying..th'e voltage betweenthc electrode` 86 andv the burner. 88 -in' a jcontinuous fashion; in

which-case the .electrode lift cam 82 will serve as a timing-means for controllngythe application of they followup voltage. It is` desirable,however,y to providean additionalfollow-up-voltage timing means, so that theA follow-up voltage is=.applied...between-the. electrodej86` and the conducting-envelope for a total period of at least 0.5 second while theA uppermost. portion Vof the electrode traversesa path defined by a vlocation proximate the neck portion148`of theenvelope 50"and a location well within theinterior-of the bnlbous portionSZ:v of. the. envelope 50.

Such ladditional voltage-timingv meansmay .besimple make-and-break contact. 90 actuated by a cam 92 on the cam shaft 26.

'In thediagrammatioview shown in FIG. 1,. the followup-voltage station` 401 has been-shownv as V comprisingtwo individualpositions;- In practice, it i`s1oftendesirable to use.only one of thev individualffollow-up voltage positions and-finy such case, the unused follow-upuvoitage position may he.` disconnected.. Of course-more than two followu-p-volta'ge positionsacoldl be used. ift" desired. Whether theffollow-up'; voltage isl applied at one or more work' positions` on. theapparatus,` the. total time for. which the voltage. isy applied inthe manner as indcatedshould be at\least.0.5 second.

- Iny the; preferred embodiment' as descrbedhereinbefore,..,the electrostatic fields are applied in such` a manner that: theirndirectionjis from the interior ofthe envelopes to .the envelope-surfaces, that is, the negative potential is applied to the electrodes at both the coating; work station 38 and the follow-up-voltage work station` and aground. potential-is applied to the envelope surfaces f throughy the:V conducting .gas flames. This causes. the electrostaticv fields to be directed` from loca-v tions within. thefinterior ofthe envelopes'tothe surface the bestcoating. Ifl'the electrodes are. made Vpositive with? respect to the envclopesnrfces, at either the coating. or foll'ow-up-'voltage work stations, or both, it has been found. thatithere'V will be small striations or. coronaappearing lines; particularly at: the neck portions of: the coated envelopes and this impairs somewhat theappearance of the finished lamps. Such striation effects, however, may` be tolerated for some applications and vthe adherence of the coa'ting'materialtothe envelopes Will beA enhanced` by the follow-up field as specified, nofmatter what the polarity ofthe electrodes with-,respect to the conducting envelopes.`

In the embodiment as shown.l in FIG. 3, the metallic electrode 86.ha sprovidcd2 over. the-lower portion thereof.` alhigh-electrical-brealrdown coating 94which may be formed. ofv quartz, for example. Suchav coating is not required,f but` it` isdesirableto provide such4 a protective coating. 94.0ver, the. portions `of` the electrode 86;` which arel proximate the neck portion- 48 of they envelope- 50 portion' 5`2of the.4 envelope 50i. provided'the electrode 86 is always. spaced. apart? from. the envelope coating.

The follow-upi'voltage' should.` be appliedi between. the

electrodefvand the conductingenvelopef 505forza` total period of atleast 0:5"secondfwhile'the electrode isfmoving-. within: the envelopez. This minimum time, forl the. application oflthe: follow-upf electrostaticr field? is necessary in order: to` enablethez adherence fofftlie; coating .material when-fthe electrode 86is positioned well'withinithe lamp v envelope. This't'endsatof minimize somewhat any.` striation-appearing; lines which are apt to occur in: the coating proximate the envelope. neckl if. a-.corona-type` discharge occurs directly from the electrode 86` to the envelope ne'ckfportion. 48 for any appreciable period off time.. The -follow-up. voltage appliedy between the electrode 861andf the'conducting surface of thecoated follow-up electrostatic field it is desirable to provide the electrodev 861 with` the high-electrical-breakdown coating 9'4.`

The improvedgadherence of the coating material.1 to

the envelope resulting from the follow-up electrostatic field is apparently due to a v,compacting or "densification of the bulk density for the coating material; In explanatrode 86 is well within the bulbous portion 52 of the tion, where coating finely-divided silica, for example which has aitrue density., of about 2.2, coating-matcrial bulk density variations of from 0.042 to 0.094 gram per`cc. have beenobserved. While ka very fluffy coating material is desirable from the standpoint of theli'ghtscattering properties of the coating, vit has been observed that. where the coating-material bulk-density approaches the lower end of the observed range, the adherence of the coating material to the envelope maybe unsatisfacenvelope 50,"preferably when the upper portion of the traveling electrode 86 is proximate the midpoint of the maximum diameter of the envelope 50. Such an interrupted follow-'up voltage maybe effected by a simple make-and-breakarrangement. Of course the total time which the'folloW-up electrostatic field is applied should tory. The foregoing follow-up electrostatic field tends tov increase somewhat the coating bulk density to-cause the coating to adhere-better. Evenwith the follow-up electrostatic field, however, the= coating bulk densities, in

the case of the specified silica vfor example, still-,normali ly do not exceed the maximum observed value of 0.094

gram per cc.

The improved adherence characteristics ofthe coating` material to the envelopeare best measured with a relatively-strong air blast,.the velocity of which greatlyexceeds the velocity-.of the puff of lill' gaswhich is forced through the tubulation during-the gas-lill stcpin the lamp fabrication. I n testing silica-coated envelopes with a high-velocity,"controlledgai-r blast, thecoated envelopes which had no follow-up voltage applied thereto displayed a blow area having a diameter of Iii/1i; inch,

that is, the diameterof the envelope sectionlfrjomwhicfi the coating wasjrem'oved by the air blast wash/V16 inch. Coated envelopes fabricated at the same time under 'the same conditions, Vbut compacted with a follow-up `elecl trostatic field as specified hereinbefore, hada Ablown areal `with al diameter A,of only inch; It is thus'apparent that the adherence of the 'coating material to the-en-` velopes is. greatly 'improved where the follow-up elecf trostatic'eld isapplied.

While lsilica has been found'tovbe the most" satisfactory bulb-coating materifal,*the foregoing process. and apparatusare notlimited tothedepositionjof silica and the following materials have been found to be. suitable for deposition withV the process and apparatus as illusted and described: alkaline-earth and magnesium stannates, oxides, carbonates and silicates;'alkaline-earth sulfates; zinc oxide; alumina; tales;I sodium or calcium 1 alumino-silica'tes (Zeolite );andi-zirconium silicate.

Of course the foregoing materials'should` be very finely divided .in order to scatter effectivelythe light and` these particles should appear substantially whiteunder reflected light in order not tojabsorb excessive amounts of light, at least where. a white-appearing lamp is to-be. produced. The average ultimate particle size Vfor the always be atleast 0.5 second.

As-'a further-embodiment, the method for increasing -the adherence of the electrostatically-deposifed coating' materialas described hereinbeforc may bc carried out by -handas well as by the apparatus described. As an cxar'nple, the coated envelope 50 could be removed from ythe electrostatic coating machine-l0 after the envelope is indexed: fromthe coatingwork station 38. The envelo'pe could then be placed by hand onto an` individual head and the electrodeV manually` reciprocated into the coat'cdevelope while the follow-up voltage asrequircd to produce the follow-.up electrostatic field was applied between the electrode-andthe conducting surface of the envelope. Thereafter,- the coated envelope could be .placedback on the machine-10 to be indexed through thc lehring and unloading stationsasindicated.

While the follow-'up electrostatic field should be applicd'fora Aperiod of atleastr 0.55 second while the electrode is vtravelling or 'moving with respect f to .the conductingcnvelope, this -peri'o'd may be extended if desired. Also, from the standpoint ofl equipment design it may be desirable tov have the electrode pause when it is fully reciprocated within the lamp envelope. During such pause, the follow-up electrostatic field may be continuedrif desired; v While in accordance .with thepatcnt statutes, one bestknown embodiment ofthe invention has been illustrated 'a-ndfdescribed inrlevtail,l it is to be particularly understood 'that the invention isnot limited thereto or thereby.

l'. The method ofincreasing the adherence of clectrostatically-depositedfinely-divided material to the interior surface of a light-transmitting glass envelope having a neck portion,` 'comprising 'heating the material-coated envelope to render it substantially .uniformly electrically conductiveva'nd applying for afperiod of at least 0.5 second al travelling high intensity electrostatic field between the envelope surface and locations within said envelope spaced from the material coating, 'including a location bounded .by the neck portion of `said envelope and a location wellw'ithin the interior of said envelope, to compact said deposited finely divided material and improve the adherence thereof torthe in-terior surface of said glass envelope. f l

vfinely-divided, light-scattering material may" vary over.

a very. wide range, such as from about 0.02 micron to about 1 micron, vfor example, and even this-range may be extended if desired. i

"It will -be recognized that theobjects of the invention have been achieved by providing a method for in-v creasing the adherence of -..electrostatically-deposited, tinely-divdedcoating material,` preferablysilica; tothe interior surface of an envelope such as anincandescent .lamp envelope, as'well as a method'fo'r electrostatically l depositing such silica material so that.itl will have very v good adherence for the envelope. In addition there has y been provided an improved incandescent lamp envelope electrostatic coating machine for producing `coatings which are very adherent to the la'mp envelopes.

As van alternative embodiment, the, follow-up velectiostatic eld may be interrupted during the period the electrode 36` is positioned :within the envelope 50. this will still result in a travelling electrostatic field.

' If such an interrupted schedule is t'o -be utilized, lthe follow-up voltage should be applied at least when the upper r .portion of the traveling electrode 8t5 is proximate the neck portion 48 of thev envelope 50 and when the elec- In effect,l

2. The method of increasing the adherence of electrostatically-deposited finely-divided light-scattering conting material to the interior surface of a light-transmitting glass envelope having. a neck portion and a bulbous portion, comprising heating the material-coated envelope to render itsubstantially uniformly electrically conductive,

v and applying for a period of at least 0.5 second a travelling high'intensity electrostatic field between the envelope surface locations within said envelope spaced from-the material coating and bounded bythe neck portion andthe bulbous portion to ,compact said deposited finely divided coating material and'improve the adher- 1 ence thereof to the interior surface of said glass enthe bulbous portion to :compact usaid .deposited tine1ydi- I vided coating material and improve :the :adherence .thereof to the interior surface :of--saidrglassenvelope. l

4. The-methodof increasingntheadherence ofelectro? i staticallyfdeposited finely-divided :light-scattering l.coating material to the interior surface of anincandescent lamp glass envelope having .a .nec-k :portion and .1a .bul-bons portion, comprising :heating ith'e materialcoated Venvelope .to render it substantially `.u`1'iiiormly- :electrically conductive, and'applying for :a .period of at :least "l0i5 `second .atravelling high intensity :electrostatic 4field .between the :envelorie` surface .and locations vwithin said .envelope positioned proximatefthe :envelopezcenter'line.and spaced from the material ycoating l:and bounded .ibyjthe neck :portion and the V.bnlbous :portion :to jcornpact .zsaid .deposited .nely

divided vcoating lmaterilarrd 1improve the adherence .thereof to the interiorsur'face `of said `tglass fenvelope.

5. The method :of :n'creasing'tthe .adherence .of electrostatically-deposited .finely-divided light-scattering .coating material .to 'the vinterior :surface .of an incandescent .lamp glass envelope having .a neck portion vand 4a gbulbous `portion, wherein the ."lines .of-force comprising the 4velectrostatic eld which effected 'the :material deposition extended from theinter'iorof the :envelope :to vthe :envelope surface, .comprising .heatingthe material-coate'd envelope to `render .it 4.substantially uniformly velectrically .con-

ductive, `and `.applying 'for .a ...total time .of .at :least v0.5

second :a `travelling iliigh intensity electrostatic `field "beof f-nely-divided .light .scattering :silica ,particles tonto V.the

interior `surface `of lan .incandescent .lamp glass envelope havingan :open `neck portion :and la vhtil'bous rportion, ,comprising heating ithe :envelope .to ,render Ait substantially uniformly electrically .conducti-v'e, ...forcing a gaseous merdium .carrying :.i'nely-.divided light-scattering :silica into said conducting :envelope Ato icharpgetat :least :a portion o'f the :finely-divided .silica carried said envelope, si-

multaneously applying .a high Jintensity .-.e'lectrostatic ,field :between ,1a .location awi'thin the interior fof said `envelope and the .envelope surface vso .that Aa .substantial portion l -of the .silica particles `carried zwithin said ,envelope will be so :attracted to .fand ,will :coat :the interior surface of the .envelope and aso that ithefauncoated remainder of vsaidxsilica particles .carried within said yenvelope will y,be carried l'by said gaseous medium :from .said envelope through fthe envelope .open *neck portion, .thereafter -`mairi- .tainingjsaid ...coated .envelope substantially :uniformly electween theenvelopeysurfacegand locations withinsaid enf velope spaced from the material r.coating fand .bounded `.by the neck portion and .the .bu'lbous 'portion vto compact said .deposited vlinely .divided .rcoatingmaterial vand improve the `adherence thereof `to 'the interior'surface `of said glass envelope, with fthe'llines :of .force vcomprising said applied field vextending Ilfrorn :the locations 'within 1.

saidenvelope ,to .the 'envelope -surface 5 6. The .method-:of .increasing :the .adherence of electro staticallyfdeposited nely-divided silica .coating vmaterial to the interior 'surface .offan incandescent lamp .glass of `force .comprising said iapplieddeld extending .from the locations within said-:envelope 4A:to jthe envelope surface. f 7. The method of .iucreasing'ithe'adherence of electrostatically deposited 'finely-.divided flight-'scattering lcoating material to Athe .interior *.surfaces fo'f `an :incandescent *lamp glass envelope l having ,a meek portion :and La bulbous :por-

coating material :and improve the .adherence thereof 'tofio the interior surfaceof-.said ,glass :envelopeywith the lines Itrically.conductive 4and .applying for .a gperiod of lat .least 0.5 `second :a travelling 1thigh intensity electrostatic eld between :the 4envelope :surface and Alocations `within .said envelope .spaced .from g'the ymaterial `coating 4and lhounded by ,the :neck portion and ithe Sbnlbousl V-portion sto :com-

pact `said `deposited (tinely `'divided coating `.material and .improve `the .adherencexthereof .toxthe interior. surface of :said V:glass envelope. w

"9. .In .combination with 1an .openinecked .incandescent lamp' glass `.envelope A.electrostatic.coating. machine having ajp'luralityof .work'stationsgincluding.an envelope pre#v :heating station, .an envelope electrostatic `.coating station .and J.a v.coated .envelope `.lehring station, together vwith means Fforv indexing .envelopes from -wok fstatiojnato work station Lin 4the 'foregoing work-station sequence, "the improvement which Lcomprisesja `follow-up-voltage 4station following said ,envelope l coating istation, said follow-upvoltage .station comprising: :fa heating Vmeansv for heating the surface of .coated l.envelopesreceived .on station to `render'same lsubstantially @uniformly `electrically conductiveiandvto ifacilitate electrical .contact to suchcoated envelopes, :a reciprocating electrode adapted `to move within coated` envelopes received on station `froma position proximate the open'necksof such .coated envelopes tov .an-extreme position well `within such coated envelopes, electrode timingimeans to control the travel of said elecitrode within coated-envelopes received on station so that said electrodemoves within such -coated envelopes for a period of at least 055 second, means'for 'applying a unidirectional high-voltage :potential lbetween said electrode and conducting envelopes Ion station -while said .electrode is' moving `within such envelopes, voltage -timlfing meansfor applying said `potential tbetween said electrode vand conducting .envelopes-ion station for .at least '0.5 second while said electrodeis within such conduct- I. ing -.envelo,p1es, .including jpositions 'proximate the *neck tion, wherein'the llines .fof force :comprising fthe electrol staticwiield `which etecte'd the v'material deposition extended'from the 'interior o'ffthe envelope `to the envelope `surface,comprisingfheatingj-.the .coated envelope to render it substantially uniformly y.electrically conductive, Aand fapf plying for a total ltime fof at.`least"0;5 second :aftravellmg high'inten'sity .electrostatictield*betweenfthe tenvelope surface Aand .locations 'within .the `:envelope Vinterior .extend-A ing from a point -proximate :the midpoint-'oftheenvelope neck portion .to a ,point fprox'imate tthe midpoint -of "the,`

maximum diameter of the renvelope btilbou's portion "to i vcompact said :deposited :'fne'ly tdivided v.coating lmaterial and improve the :adherence ithereof ltoithe 'interior surfact of said .glass envelopexwith fthe Ilines of Aforce 'comprising said .lappliedield (extending from-.the Elocations Within said y.envelope tofthefenvelope surface.

8. method-ici felectrostaticlly depositing `a coating "portionof such .envelopes and well within such .envelopes, means f orLholding-coated:envelopes'in position on station, `and imeans for indexing lcoated envelopes to and frorntstation.-

K `flt). In.,cornbina'tion wwith anopen-necked incandescent :lamp glass -envelope electrostatic coating machine .having .a.1p1urality*16f'wok .stations including Van .envelope prehating station, `an :envelope electrostatic .coating lstation-fand Aa coated: envelope lehring station, `together with `meansffor `:indexing envelopes from =.wor'k vstation -to vwork station inf'the .foregoing work-station sequence, the -improvement'` which comprises a vfcillow-up-voltage station following ysaid envelope coating station, said follow-upvoltage y station comprising: gasfair :burner Yheating `means for heating :thegsurface of coated envelopes received `on station jt'o `render same vsubstantially `.uniformly electrica1ly`=conductive and -vto "facilitate v.electrical Contact tov such coated ',envelopes, a lreciprocating electrode .adapted to .move-within each-coated .envelope freceived on :station ,from I.apo'sition proximate the midpoint `of lthe yopen-necks fof tsuchacoated @envelopes tto .an extreme position :protei- 1l mate the midpoint of the maximum diameter of such coated envelopes, eleetrode'timing means to control the travel of said electrode within coated envelopes received on station so that said electrode' moves within suchl coated envelopes for-a period'of at least 0.5 second, means for applying a unidirectional high-voltage'potential between said electrode and theI conducting envelopes onstation while said. electrode is moving within suchenvelopes with v'the lines of=force comprising the resulting .electrostatic eld ex'tending'from said electrode to suchgconducting envelopes, voltage timing `means foi` applying said potential between said electrode and con'-A ductingenvelopes on stationfor at least 0.5 second while said electrode is lpo'sitionedwvithin such conducting envelopes and traverses 'a path defined by electrode positions proximate the neck of such envelopes andl proximate the midpoint of themaximum diameter oisuch envelopes', means for holdingi'coated envelopes received heating station, 'an envelope electrostatic coating station and afcoated envelope lehring station, together with means for indexing envelopes from work"A station to work station in the foregoing work-station sequence, the improvement coated envelopes, means for holding coated envelopes in position on station and for effecting a -rotation between such coated envelopes and said gas-air burner heating' means when' said electrode is moving within suchcoated envelopes and voltageis applied thereto, and means for indexing coatedv envelopes to and from station.

11. In combination withan open-necked incandescent lamp glass envelope electrostatic coating machine having a plurality of work stationsincluding 'an envelope pre heating station, anl envelope electrostatic coating station and acoated envelope lehring station, together with means for indexing envelopes from work station to work station vin the foregoing work-station sequence, the improvement station to render same substantially uniformly electricallyV conductive and to `facilitate electrical contact to` such coated envelopes, va reciprocating velectrodeadapted to move within-'each of the coated envelopes received on station from a position, proximate themidp'oint-of the open necks of vsuchcoatedv envelopes. toan extreme .position well within snch coated envelopes, 'a'high-electricalbreakdown c'oating'provided 'over. the portions of said which 'comprises a followup-voltage station comprising .at least one follow-up-voltageposition following said envelope coating" station, each said follow-up-voltage position comprising: a heating means for` heating the surface of received coated envelopes to render same substantially uniformly electrically conductive and to facilitate electrical contact to such coatedenv'elopes, reciprocating electrode means adapted to project within each received coated envelope from a position proximate the-midpoint of the, open necks of such `coated envelopes tov an extren-ie position well'within such coated envelopes, timing means to controlthe travel of said electrode means within received coated envelopes from a position proximate the midpoint of the open necksv of such conted' envelopes to an extreme position Well' within such coated envelopes, timingv means to control the ltravel oflsaid electrode means within -received coatedenvelopesso that said elec trode (means moves withinisuch coated ,envelopes for a period ofat.leas t' 0.5"second, means for applying a unielectrode whichf'are adjacent the necks of coated envelopes received on station when said electrode is -projectedwell within such coated envelopes, electrode timing means to control ,the travel ofsai'd-Ielectrode within coated envelopes received on station so that said electrode moves coated envelopes on. station while said electrode is moving within such envelopes, voltage timing means forapplyving said potential betweensaid electrode and conducting envelopes on station for' at least 0.5 second while said tfystrode isfpositioned within such conducting-envelopes and traverses a path detin'ed by'electrode positions proximate the necks of such envelopes andwellsuch directional high-'voltage potential between said electrode means and received. conducting envelopes while said electrode ,means is moving within such envelopes, voltagel'timing means forv applying saidpotential between said .electrode means andlreccived conducting envelopes for at least' 0.5 second while said electrode means is positioned within such;conducting4 envelopes and traverses-a path d ened by electrode positions proximate' the necks of such envelopes and well within such envelopes, means for holding received coated envelopes in position and for effecting a rotation .between such coated envelopes andsaid heating means when said electrode means is'moving withinf'such coatedenvelopesand voltage is applied thereto,

and means for indexing coated envelopesto and from the individual follow-up-voltage positions comprising said followup-'voltage station-and to and from said follow-upvoltage station.

'l References Cited4 inthe file of this patent UNITED STATES PATENTS 2,806,444 vwerner et; al. sept. 17, 1957 l 2,811,131 4' Lopenski et al. ..-e Oct. 29, 1957 

1. THE METHOD OF INCREASING THE ADHERENCE OF ELECTROSTATICALLY-DEPOSITED FINELY-DIVIDED MATERIAL TO THE INTERIOR SURFACE OF A LIGHT-TRANSMITTING GLASS ENVELOPE HAVING A NECK PORTION, COMPRISING HEATING THE MATERIAL-COATED ENVELOPE TO RENDER IT SUBSTANTIALLY UNIFORMLY ELECTRICALLY CONDICTIVE, AND APPLYING FOR A PERIOD OF AT LEAST 0.5 SECOND A TRAVELLING HIGH INTENSITY ELECTROSTATIC FIELD BETWEEN 